In a medical field, ultrasonic diagnostic apparatuses are widely used, such an apparatus transmits and receives ultrasonic waves by using an ultrasonic probe with respect to a subject, so that it obtains information about the respective parts of the subject, depending on the acoustic characteristics of the parts. In the ultrasonic diagnostic apparatus, a transducer array as an ultrasonic element for transmitting and receiving ultrasonic waves is used, and this transducer array is oscillated mechanically to change the surface to be scanned with the ultrasonic waves, thereby obtaining three-dimensional information of the subject.
The probe used in such an ultrasonic diagnostic apparatus generally includes an ultrasonic element and an oscillation mechanism for oscillating the ultrasonic element. The oscillation mechanism is configured, for example, by connecting a supporting axis to an output axis of a motor via a gear and connecting to this supporting axis a holder that holds the ultrasonic element. In the oscillation mechanism, when the motor is driven, the rotatory power is transmitted to the supporting axis via the gear so as to cause rotation to the supporting axis, thereby the ultrasonic element rotates with the holder, in synchronization with the movement of the supporting axis. By reversing the rotating direction of the motor at predetermined time intervals so as to reverse the rotating direction of the ultrasonic element, oscillation of the ultrasonic element is provided.
Furthermore, the oscillation mechanism provided with an angle detector to detect oscillation angle of the ultrasonic element has been proposed (for example, see JP3(1991)-184532A). FIG. 7 is a perspective view showing the structure of the angle detector which composes a conventional ultrasonic probe. The angle detector 70 is composed of a slit plate 72 which rotates together with the supporting axis 71 and has plural slits arranged concentrically about the rotating axis, and an optical counter 73 arranged pinching the slit plate 72. The optical counter 73 is divided at the slit plate 72 into two parts: one is for emitting light and the other is for receiving light that has passed through the slits. Based on the number of the light reception counts, the rotation angle of the slit plate 72, that is, the rotation angle of the supporting axis 71 is detected. By detecting the rotation angle of the supporting axis as above, the rotation angle (the oscillation angle) of the ultrasonic element which rotates together with the supporting axis can be detected as well.
In the conventional ultrasonic probe, however, the detector detects only the number of light reception counts, thus it has been impossible to detect accurately an oscillation origin or the position of the ultrasonic element at the time of turning on a switch with respect to the ultrasonic probe. This has caused a problem that control of origin return of the ultrasonic element would be complicated, thus delaying a time for the origin return.